I'm not sure what the internal/system 'facebook' custom field is - but if it's there with such a generic name, we should be able to use it... is it a username, a profile ID, a Profile link, a Page link, a Group link?
How does it get populated?
How would we ever update outdated information if we cannot view/edit this field?
We should be able to create a 'facebook' custom field (so the field name is not reserved) or access the built-in system one.
Ticket# 282052